Hydraulisches Steuerungssystem eines stufenlosen Keilriemengetriebes mit einer ausfallsicheren Schutzanordnung.

摘要

An apparatus for controlling a vehicle continuously variable transmission (14), including a directional control valve (262) having a first spool (280) movable between a shift-down and a shift-up position, a flow control valve (264) including a second spool (288) movable between a flow-restricting and a non-restricting position, and a first and a second solenoid-operated valve (266, 268) for applying an actuating pressure to the first and second spools. The directional and flow control valves and the solenoid-operated valves are adapted such that the first and second spools are moved toward the shift-up and flow restricting positions, respectively, when the actuating pressure is not applied to the spools, or when solenoid coils of the two solenoid-operated valves are both off. The directional control valve may have a shift-down chamber (283) for receiving a pilot pressure (Psol5) to move the first spool to the shift-down position when a failure of one of the solenoid coils exists while the vehicle speed is lower than a predetermined limit.